Making malleable-iron castings



till? Patented 0a. 23, 1928.

UNITED STATES PATENT OFFICE.

HARRY A SCHWARTZ, CLEVELAND HEIGHTS, OHIO, ASSIGNOR TO NATIONAL MALLE- ABLE AND STEEL CASTINGS COMPANY, OF CLEVELAND, OHIO, A CORPORATION 03' OHIO.

MAKING MALLEABLE-IRON CASTINGS.

No Drawing.

My invention relates to the treatment of iron in converting it into malleable iron castings, and particularly to the quenching of the iron in such a way as to accelerate greatly the annealing or alleableizing cycle and improve the resulting product.

I have found that if, when the metal is cast, oris reheated to a high temperature after the casting operation, itis cooled with sufiicient rapidity from any temperature above the critical point to any temperature below the critical point, the subsequent annealing will be much more rapid than if the casting had been cooled in the usual way, and the separation or precipitatlon of the graphite for a given time will be much more complete than with usual annealing.

A typical example of carrying out my invention is to quench the iron either shortly after casting and when it is still above the critical point, or after the casting has been reheated to a point above the critical temperature for a sufficient time for the casting to become heated to an eventemperature throughout. This quenching may be done in.

oil or water. I have obtained satisfactory results where the cooling rate down through the critical point was a proximately 10 F. or faster er second. he cooling is carried on prefera ly but not necessarily at the same rate until the castings have been cooled, possibly to room temperatures if the castings are of a form and composition which are not liable to crack, or the cooling may be stopped in a considerably higher ran e, such, for instance, as from 400 to 600 to guard against cracking. The castings may then be reheated immediately to a suitable temperature .for annealing, and preferably to a temperature above the critical pointthat is, to a temper ature of about 1650 F.which is usually attained in ordinary annealing practice. They should be held at that temperature for a suf-.

ficient time to permit the decomposition of the cementite. Such-time. in carrying out my invention is much less than the time usual for carrying out the normal annealing cycle, perhaps only from a tenth to a quarter as long as would be required to produce the same result by any of the present well known methods. I have found, for instance, that five and a half hoursis a suficiently long time for holding most commercial white cast irons at that temperature. It is well known that va- Application filed December 23, 1926. Serial No, 156,761.

rious grades and compositions of white iron diifer enormously among themselves with respect to the time required to secure the decomposition of the cementite, but irrespective of whether this time be normally long or short, I have found that my prequenching treatment reduces the required time in approximately a constant proportion. I have also found not only that the rate of graphitization and consequently the annealing time depends on the hard iron under treatment, but also upon the rate of prequenching. In other words, the faster the prequenching rate, the faster is the graphitizing rate. My invention is therefore extremely valuable not only with the usual grades of commercial white cast irons, but also with grades which are normally slow to graphitize.

After holding the casting at the high temperature stage of the annealing cycle for a period which may be not more than three to ten hours (which usually has been found to be a suflicient length of time to effect graphitization with normal commercial irons), the casting is cooled down to just below the critical point as rapidly as is. convenient. The rate, of course, depends on the particular kind of annealing furnace employed. The casting is then held at a temperature distinctly below the critical point for a period of approximately thirty hours, to break down the re- -maining combined carbon. Thereafter it "may be cooled in any suitable way, as by Iron which has been annealed, in the man-,

ner described above, after the prequenching treatment, shows an unusually fine distribution of carbon. There'is some indication that this is because the treatment described pro- 'duces a finer dispersion of cementite in the areas which were originally pearlitic, and that this finer dispersion, as it for'in's ,more surface of contact between cementiteand solid solution and hence perhaps the formation of more graphite nuclei, may be the cause of the acceleration of the graphitization.

In addition to quenching before the annealing cycle, thccastings can, if desired, be quenched at the end of the high temperature phase of that'eycle. Such a quenching has the beneficial result of increasing the, rate of decomposition of the remaining combined to be practicable from a commercial standpoint by reason of the fact thatit is a very slow operation. When, however, the iron is prequenched as described above, the annealing cycle just referred to is sufficiently speeded up by the prequenching treatment so as to make it commercially practicable. The prodduct of such an operation is superior in ductility to the usual malleable iron castings.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have nointention, in the use of such terms and expressions, of excluding any equivalentsof the features described, or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

What I claim is:

1. That improvement in the art of making malleable iron castings which comprises taking an iron containing carbon, silicon, phosphorus and sulphur 1n the proportlons normally found in a malleable cast iron .at a

temperature above its critical point, cooling the iron rapidly from a tem erature above such point to a temperature be 0W that point, subjecting the casting to an annealing cycle which comprises reheating the casting to a temperature iabove the critical point, holding it at such te' perature for a period of time sufiicient 'to reak down the cementite, then cooling to below the critical point.

2. That improvement in the art of making malleable iron castings which comprises taking an .iron icontaining carbon, silicon, phosphorus and sulphur in theproportions normally found in a malleable cast iron at a temperature above'its critical point, cooling the iron rapidly from a temperature above such point to a temperature below that point, subecting the castm to an annealing cycle which comprises reheating the casting to a temperature above the critical point, holding it at such temperature for a period of time sufiicient to break down the cementite, then cooling to below the critical point, holding the casting at a temperature below the critical point, and then cooling;

'3. That improvement in the art of making malleable iron. containing carbon, silicon, phosphorus and "sulphur in the proportions normally found in a malleable cast iron castings which comprises taking the iron at a temperature above its critical point,.cooling the iron rapidl from such temperature to a temperature elow that point, annealing the casting by heating it to a temperature appreciably above the critical point, holding it at that temperature for a sufficient time to the casting by heating it to a temperature'appreciably above the critical, point, holding it at that temperature for a suflicient time to break down the cementite, then cooling the casting rapidlyto below 600 131., and then reheating to distinctly'below the critical point, holding it at that point for a considerable period of time to break down the remaining combined carbon, and then cooling.

5. That improvement in the art of making malleable iron castings which comprises taka ing an iron containing carbon, silicon, phosphorus and sulphur inthe proportions nor-' mally found in a malleable cast iron at a tem perature above its critical point, cooling it from such temperature at a rate of at least 10 F. per second to a temperature below the said critical point, and then subjecting the casting to an annealing cycle comprising reheating the casting to a temperature above the critical point, holding it at such temperature for a period of time sufiicient to break down the cementite and then cooling to below the critical point. a

i 6. That improvement in the art of making malleable iron castings which comprises taking an iron containing carbon, silicon, phosphorus and sulphur in the proportions normally found in a malleable cast iron at a temperature above its'critical point, cooling it rapidly from such temperature'to a temperature below the critical point and further cooling it to at least 600 F., then reheating to. a temperature above the critical point, holding it at that temperature for a period of approximately three to ten hours to effect destruction of the cementite, and then cooling to below the critical point;

7. That improvement in the art of making malleable iron castings which comprises taking an iron containing carbon, silicon, phosphorus and sulphur in the proportions normally found: in a malleable cast iron ata tem perature above its critical point, cooling the iron rapidly from a temperature above such point to a temperature below that point, subjecting the casting to a further heat treat- I ment for the purpose of efiecting the graphitization of itscombined carbon.

8. llhat improvement in the art of making malleable iron containing carbon, silicon, phosphorus and sulphur in the proportions normally found in a malleable cast iron castin 's which comprises taking the iron at a temperature above its critical point, cooling {the iron rapidly from a temperature above such critical point to a temperature below such point, subjecting the casting to a further heat treatment for the purpose of graphitizing the combined carbon,' the graphitizing rate being materially afiected by the cooling rate by which the casting Was cooled prior to the graphitizing treatment.

9. That improvement in the art of making malleable iron castings which comprises taking an iron casting produced in a sand mold and containing silicon in the amount normally found in a malleable iron, at a temperature above its critical point, cooling the iron rapidly from a temperature above such point to a temperature below that point, subjecting the casting to an annealing cycle which comprises reheating the casting to a temperature above the critical point, holding it at such temperature for a period of time suflicient to breakdown the cementite, then cooling to below the critical point.

HARRY A. SCHWARTZ. 

